Assessment of Calculation Procedures for Piles in Clay Based on Static Loading Tests

Numerous methods are available for the prediction of the axial capacity of piles in clay. In this paper, two well-known models are considered, namely the current API-RP2A (1987 to present) and the recently developed ICP method. The latter is developed by Jardine and his co-workers at Imperial College in London. The calculation procedures are assessed based on an established database of static loading tests. To make a consistent evaluation of the design methods, corrections related to undrained shear strength and time between pile driving and testing have been employed. The study indicates that the interpretation of the field tests is of paramount importance, both with regard to the soil profile and the loading conditions. Based on analyses of 253 static pile loading tests distributed on 111 sites, API-RP2A provides the better description of the data. However, it should be emphasised that some input parameters in the ICP method have been estimated based on relatively uncertain correlations, which might affect the results. The ICP method could preferably be applied for piles loaded in tension. However, it is recommended not to use the ICP method for piles driven open-ended and loaded in compression. Especially, API-RP2A underestimates the capacity of short piles (< 20 m) and overestimates the capacity of long piles (> 20 m). Neither method estimates the low shaft resistance measured in connection with piles installed in normally consolidated clay of low plasticity.